You've obviously put alot of tought into how you're gonna play this list.
I don't have the expirience needed to predict how this style of play will do against spesific types of opponents, but what I can say is that this is seemingly the most tought out list I've seen on the eldar forum in the weeks I've been here.
It's the first list I've seen where the Avatar acually has a purpose, and the first "slow" list I've seen that acually makes somewhat sense to me. So, thanks for the read.

Have you tried using the defend exarch power for the Avengers?
Seems to me that if there is a list where it would be useful, it would be this one. Perhaps it would even be beneficial to tool one of the Avenger squads with a power sword and a shimmershield, for the added menance against close combat marines, chaos and the like? It would also give you better options in controlled retreats and in cat-and-mouse games.

You may find that the troupee master of the Harlequins is unnessesary, while the 6 man squad may need a few more hugs and kisses instead.

Seems to me your falcons would do better with scatter lasers, but I bet you've heard that before?

The more i look at that list the more i like it actually, flying in the face of the mechanised trend.
You may suffer on low terrain tables but otherwise it seems really solid.
As drax said, maybe one Avenger squad with the more shimmershield/defend combo to play point for your avenger group to act as an anvil for fast melee opponents so your Harlequins and Scorpions can play hammer on the countercharge.
Thats my only other point, the Scorpions could find themselves a bit isolated playing infiltrator all alone with no fast backup coming and i might be inclined to go with Banshees who could keep up with the Avenger wave and provide that bit of extra punch against those MEQ type opponents, but thats purely a preference and hardly a make or break factor.
Nice list, i'm rather inspired to try something similar myself...

I for one like this list. Dire avengers are freaking awsome!!! and like was said earlier its great to see a troop heavy list in the face of the Mechanized lists all too popular. The only thing that I might do different is to take out the Avatar (too bad we can't have 3 HQ's) and throw in a second Farseer = 2x more doom, 2x more guide!!! which means 2x more death!... Just a thought what does eeryone else think?

Veni Vidi Vici
"The plan is to win, if we don't win its cause you guys didn't follow the plan!"
Eldar: 25,000 pts

The Avatar is obviously there to make everyone fearless, which should be great for this particular list.

There is nothing quite worth guiding in this list, and while doom is great I can't see how it would be worth the points with the Farseer being on foot and all. If I was going to play this list, I'd rather take out the Farseer for once and leave the Avatar as the sole HQ pick. But that's just me.

as pooka pointed out the obvious change that needs to be made to the list is to switch out guide for fortune and make sure to get the farseer spirit stones so that he can use both powers every turn.

also, statisically against marines scatter lasers get almost the same number of kills as starcannons but offer increased volume of fire which helps out more against GEQ and against light vehicles. I would definitely make the swap though I tend to run my falcons with dual shuriken cannons to keep them on the cheaper side.

I would be tempted to say drop another three kisses off of the first harlie squad ( you do not want them killing the enemy off entirely on the charge) and the troupe master to upgrade another one of your DA squads to have defend and PW+SS, otherwise looks great!

I would keep pathfinders out of this list as they are likely going to be left behind and as such find themselves being threatened without any back up.

EDIT: Also, where are the spirit stones on the farseer? Without them he is limited to casting one power a turn...